In fields such as semiconductor manufacturing, nanoimprint methods have begun to attract considerable attention as a technology that is capable of forming ultra fine patterns of 100 nm or less and providing excellent mass production applicability at minimal cost. In a nanoimprint method, a mold which has a pattern of protrusions and recesses to be transferred is pressed against a transfer target material composed of a photocurable resin or a thermosetting resin, and the transfer target material is then cured by the irradiation of light or application of heat, thereby transferring the pattern to the transfer target material. Of such methods, transfer methods that use a photocurable resin are referred to as photo nanoimprint methods, whereas transfer methods that use a thermosetting resin are referred to as thermal nanoimprint methods.
The nanoimprint mold having the fine transfer pattern formed thereon is generally formed from silicon, a silicon oxide, nickel or quartz glass or the like. Further, as the transfer target material, thermoplastic resins such as poly(methyl methacrylate) (PMMA) and polyimides (PI), photocurable resins such as polyester alkyd resins (PAK), and high-viscosity resins such as hydrogen silsesquioxane resins (HSQ) and spin-on-glass (SOG) materials are often used.
In recent years, the range of applications for magnetic recording devices such as magnetic disk devices, flexible disk devices and magnetic tape devices has expanded enormously, and the importance of such devices continues to increase. At the same time, the recording density of the magnetic recording media used in these devices has also required to increase markedly. Particularly since the introduction of magnetoresistive (MR) heads and PRML techniques, the increase in surface recording densities has become even more dramatic, and the more recent introduction of giant magnetoresistive (GMR) heads and tunnel magnetoresistive (TMR) heads and the like has meant that recording densities continue to increase at a pace of approximately 100% per year. However, there are strong demands for even higher recording densities for these magnetic recording media, and meeting these demands requires further improvements in the coercive force and signal to noise ratio (SNR) of the magnetic layer, and higher levels of resolution. Furthermore, in recent years, concurrently with the improvements in linear recording density, efforts are also continuing into raising the surface recording density by increasing the track density.
In the most recent magnetic recording devices, the track density has reached 110 kTPI. However, as the track density is increased, mutual interference tends to occur between the magnetically recorded information within adjacent tracks, and the resulting magnetized transition region in the boundary region between the tracks acts as a noise source, causing problems such as a deterioration in the SNR. This reduced SNR leads directly to a deterioration of the bit error rate, and is therefore an impediment to achieving increased recording densities.
In order to increase the surface recording density, it is necessary to reduce the size of each recording bit on the magnetic recording medium, and maximize the saturation magnetization and magnetic film thickness for each recording bit. However, as the recording bits are reduced in size, the minimum magnetization volume per bit is reduced, and a problem arises in that recording data may be erased due to magnetization reversal caused by heat fluctuation.
Further, because the distance between tracks narrows, the magnetic recording device requires extremely high-precision track servo technology, and in addition to employing such technology, a method is usually employed where recording is executed over a comparatively wide range, and reproduction is then executed across a narrower range than that used during recording in order to exclude, as far as possible, effects from adjacent tracks. Although this method enables inter-track effects to be suppressed to a minimum, achieving a satisfactory reproduction output level can be difficult, and therefore ensuring an adequate SNR is also difficult.
One method that is being investigated as a method capable of addressing the above problem of thermal fluctuation, ensuring a satisfactory SNR, and achieving a satisfactory output is a method in which the track density is increased by physically separating adjacent recording tracks, either by forming a pattern of protrusions and recesses (in which the peaks and depressions may also be referred to as “lands and grooves”) that coincides with the track pattern on the magnetic recording medium, or by forming a non-magnetic portion between adjacent tracks. Hereinafter, this method is referred to as the discrete track method.
One example of a known discrete track magnetic recording medium is a medium in which a magnetic recording medium is formed on a non-magnetic substrate which has a pattern of protrusions and recesses on the surface thereof, thereby forming magnetic recording tracks and servo signal patterns that are physically separated from each other (for example, see Patent Document 1).
In this magnetic recording medium, a ferromagnetic layer is formed on the surface of the substrate having a plurality of lands and grooves, with a soft magnetic layer disposed therebetween, and a protective film is then formed on the surface of the ferromagnetic layer. In this magnetic recording medium, the magnetic recording regions are formed on the land regions, and are magnetically separated from the surrounding regions.
According to this magnetic recording medium, the occurrence of magnetic domain walls within the soft magnetic layer can be inhibited, meaning thermal fluctuations are less likely to have an effect, and because there is no interference between adjacent signals, a high-density magnetic recording medium that suffers minimal noise can be formed.
Discrete track methods include methods in which a magnetic recording medium composed of a plurality of thin films is formed, and the tracks are then formed, and methods in which a pattern of protrusions and recesses is first formed, either directly on the substrate surface or within a thin layer provided for the purpose of track formation, and thin film formation (magnetic layer formation) of the magnetic recording medium is then conducted (for example, see Patent Document 2 and Patent Document 3). Of these, the former method is referred to as a magnetic layer processing method, whereas the latter is referred to as a pre-emboss method.
In the latter pre-emboss method, physical processing of the substrate surface is completed prior to formation of the medium. This offers the advantages that the manufacturing process can be simplified, and that the medium is resistant to contamination during the manufacturing process. However, the shape of the pattern of protrusions and recesses formed on the substrate is inherited by the subsequently deposited films, and as a result, a problem arises in that the floating position and floating height of the recording/reproducing head that performs recording or reproduction while floating across the surface of the medium cannot be stabilized.
One example of a method that has been proposed for manufacturing a magnetic recording medium using the former magnetic layer processing method is a method that uses the nanoimprint method described above in a similar manner to that employed for semiconductor manufacture. Specifically, a method has been proposed in which a continuous magnetic layer deposited on a substrate is processed to form a magnetic recording track pattern or bit pattern using a nanoimprint method.
As described above, the nanoimprint method is a method in which a mold having a pattern of protrusions and recesses that is to be transferred formed on the surface thereof is pressed against a transfer target material, and the transfer target material is then cured by the irradiation of light or the application of heat, thereby transferring the pattern of protrusions and recesses to the transfer target material.
The mold for nanoimprinting is, for example, a mold prepared by forming an ultra fine pattern which has recessed and protruding portions and is 100 nm or less in the surface of a silicon material or the like, and is very expensive. If this mold suffers abrasion or damage during the imprint process, then the mold must be replaced, which results in an increase in the manufacturing cost of the magnetic recording medium product or semiconductor or the like manufactured using the nanoimprint method. Accordingly, in those cases where the nanoimprint method is employed in an industrial setting, a replica mold is usually manufactured in order to preserve the master mold. In other words, the pattern of the master mold is transferred to another material using a stamper device, enabling a plurality of replica molds to be manufactured from a single master mold.
Because these replica molds are produced in large quantities, they are inexpensive. Consequently, if a replica mold is used as the stamper in a nanoimprint process, then even if the mold is damaged, it can be simply replaced with another replica mold, meaning the valuable master mold can be preserved. As a result, a product which has a fine pattern of protrusions and recesses formed thereon can be manufactured at low cost using the nanoimprint method.
The use of resin molds as the replica molds manufactured using the method outlined above is currently under investigation, and for example, methods of transferring a fine pattern using a photocuring reaction (for example, see Non-Patent Document 1) and methods of suppressing shrinkage during such photocuring (for example, see Non-Patent Document 1) have been disclosed.
As a result of demands for finer processing during the manufacture of semiconductors and magnetic recording media, there are increasing demands for the formation of ever finer patterns on nanoimprint molds. For example, when manufacturing a magnetic recording medium or the like using the nanoimprint method, making the magnetic recording pattern finer in order to achieve increased recording density requires that a finer pattern is formed on the nanoimprint mold.
However formation of a finer pattern on the nanoimprint mold tends to accelerate abrasion of the mold and increase the frequency of mold damage. Moreover, because the lifespan of a resin replica mold is shorter than that of a metal mold, if a resin mold is to be used, then it is necessary to ensure that a large number of replica molds is available. Accordingly, it is desirable that the replica molds are able to be manufactured in a large quantity at a good level of productivity.
The material to which the pattern of the master mold, which has recessed and protruding portions, is to be transferred must exhibit curability, good flexibility and superior filling properties, and have a uniform thickness. One possible method for satisfying these demands is a method in which a gel-like curable resin is printed onto a base film, and this printed film is then used as the transfer material into which the master mold is pressed.
In order to ensure that the printed film is retained in a film-like form of uniform thickness, it is necessary that the resin being printed has a certain degree of viscosity. However, if this viscosity of the curable resin increases, then the ability of the resin to fill the gaps within the pattern of protrusions and recesses during pattern transfer from the master mold tends to deteriorate, resulting in a deterioration in the precision of the transfer.
Further, another possible method involves providing weirs in advance on the surface of the base film, pouring a liquid curable resin into the well inside the weirs, and then stamping the master mold onto the resulting curable resin layer. However, this method tends to require large manufacturing equipment, and has a low level of productivity. Moreover, obtaining a uniform thin layer using this type of method tends to be difficult.
Furthermore, yet another method involves using spin coating to form a thin film of a curable resin on a base film, and then using this thin film as the transfer material into which the master mold is pressed, but this method tends to require even larger manufacturing equipment, and suffers from inferior productivity.
Accordingly, the productivity cannot be improved with these methods, and the precision of the pattern transfer may deteriorate. As a result, if a semiconductor is manufactured using the nanoimprint method, then in a similar manner, the productivity of the semiconductor cannot be improved, and the precision of the pattern transfer tends to deteriorate. Moreover, if a magnetic recording medium is manufactured using the nanoimprint method, then the recording density of the magnetic recording medium tends to worsen, and the productivity may deteriorate.